Gas turbine engines are known to include a compressor section for supplying a flow of compressed combustion air, a combustor section for burning fuel in the compressed combustion air, and a turbine section for extracting thermal energy from the combustion air and converting that energy into mechanical energy in the form of a rotating shaft. Many components that form the combustor and turbine sections are directly exposed to hot combustion gasses, for example, the combustor basket and liner and nozzles, the transition duct between the combustor and turbine sections, and the turbine stationary vanes and rotating blades and surrounding ring segments.
It is also known that increasing the firing temperature and the combustion gas can increase the power and efficiency of the combustion turbine. Modern high efficiency combustion turbines have firing temperatures that exceed temperatures of about 1,600° C., and even higher firing temperatures are expected as the demand for even more efficient engines continues. Thus, the cobalt and nickel based superalloy materials traditionally used to fabricate the combustion turbine components used in the hot gas path section of the combustion turbine engine must be aggressively cooled and/or insulated from the hot gas flow in order to survive long term operation in this aggressive high temperature combustion environment.
Notwithstanding these protective efforts, the combustion turbine components nonetheless tend to suffer operational damage such as thermal fatigue, oxidation, corrosion, creep and the like, which typically causes cracking and spallation of the superalloy and/or protective ceramic coating. To further complicate matters, these cracks and spallation are caused by a variety of factors and formed in a variety of locations. For example, channel cracks can form on an interior cooling channel of the component and propagate to the component surface due to component weakness near the hollow channels.
Since these high temperature resistant components are quite expensive, it is often desirable to repair rather than replace damaged components. Several repair methods are conventionally used to repair such cracked or spalled combustion turbine components. For example, gas tungsten arc welding, laser welding, diffusion brazing and wide gap brazing are used for crack repair. If a welding technique is used, each particular welding technique has its own advantages and disadvantages.
Accordingly, there is a need for an improved method of repairing cracked or spalled combustion turbine components. There is also a need for an improved welding technique for the repair of cracked combustion turbine components.